This invention relates to an ignition coil assembly for an internal combustion engine.
FIG. 18 is a sectional view showing a conventional ignition coil assembly for internal combustion engines. In FIG. 18, reference numeral 1 designates; a primary coil; 2, a primary bobbin on which the primary coil 1 is wound; 3, a secondary coil; 4, a secondary bobbin on which the secondary coil 3 is wound; and 5a and 5b, core elements, which are formed by dividing one core into two parts each having two abutting end faces. Those core element 5a and 5b are abutted against each other through their abutting end faces on both sides, thus forming the original core which provides a closed magnetic circuit. More specifically, the abutting end faces of the core elements 5a and 5b on one side are joined, for instance, by welding, and the remaining abutting end faces on the other side are coupled through a spacer 10 to each other, thus having a predetermined gap therebetween. Further in FIG. 18, reference numeral 6 designates a connector, to which both ends of the primary coil 1 and the low-voltage-side terminal of the secondary coil 3 are connected; 7, a high voltage terminal, to which the high-voltage-side of the secondary coil; and 8, a casing, in which the primary coil 1 and the secondary coil 3 are accommodated. The casing 8 is combined with the primary bobbin 2, thus forming a container. The primary coil 1 and the secondary coil 3 are sealingly held in the container with an insulating resin 9 injected into it. In order to prevent the insulating resin 9 and the metal core 5, which are greatly different in thermal expansion coefficient from each other, from directly contacting each other, the primary bobbin 2 of resin is interposed therebetween. That is, the primary bobbin 2 thus provided prevents the insulating resin 9 from being cracked by thermal shock.
The conventional internal combustion engine ignition coil assembly thus formed operates as follows:
When the application of a primary current from a power source (not shown) to the primary coil 1 is interrupted being controlled by a power transistor unit (not shown), the magnetic flux in the core forming the closed magnetic circuit is changed, so that a high voltage is induced in the secondary coil 3. The high voltage thus induced is applied through a high voltage terminal 7 and a high voltage cable (not shown) to an ignition plug (not shown). In order to prevent the leakage of the high voltage induced in the secondary coil to other parts, the primary coil 1 and the secondary coil 3 are sealingly held and insulated from each other with the insulating resin 9.
In the internal combustion engine ignition coil assembly shown in FIG. 18, the primary and secondary coils are set in the casing, and then sealingly held and insulated from each other with the insulating resin injected thereinto. The casing has a hole in the bottom through which the core is passed through. Therefore, in order to prevent the leakage of the insulating resin through the gap between the core and the casing, the following method is employed. That is, the casing is made annular in section by fixedly bonding the primary bobbin to the casing with adhesive in such a manner that the primary bobbin defines the inside diameter of the casing, and the core is inserted into the primary bobbin thus fixed. Hence, the conventional internal combustion engine ignition coil assembly suffers from the following difficulties: That is, it is necessary to bond the primary bobbin to the casing with adhesive, and solidification of the adhesive takes time. This means that the ignition coil assembly is low in assembling efficiency. Sometimes the adhesive flows other parts in the ignition coil assembly. If the adhesive applied is not completely solidified, then it may leak out of the ignition coil assembly.
Furthermore, in the conventional ignition coil assembly, as was described above the two core elements are abutted against each other through their abutting end faces in such a manner that the abutting end faces on one side are joined directly to each other, while the remaining abutting end faces on the other side are coupled through the spacer to each other, thus providing the predetermined gap. Hence, in manufacturing the ignition coil assembly, the two core elements are abutted against each other with the spacer and the adhesive held between the abutting end faces, and in solidifying the adhesive, and in injecting and solidifying the insulating resin, it is necessary to use a certain jig to accurately support the end portions of the two core elements on the side where the gap is provided. Therefore, troubles due to errors, for instance, in insertion of the spacer are liable to take place. Thus, the conventional ignition coil assembly is low in assembling efficiency.
Accordingly, an object of this invention is to eliminate the above-described difficulties accompanying a conventional ignition coil assembly for internal combustion engines. More specifically, an object of the invention is to provide an ignition coil assembly high in reliability for an internal combustion engine which can be assembled with high efficiency and at low cost, and to provide a method of manufacturing the ignition coil assembly.